Light emanating from light sources used with photographic enlargers is usually characterized by nonuniform, random energy distribution over a transverse planar area disposed perpendicularly to the axis of the light path. It is desired to provide light which is evenly distributed over such a transverse plane to the axis of the light path in order to uniformly illuminate a film negative being enlarged. Various constructions of light mixing devices have been proposed.
In one prior proposed light mixing device, light emanating from a light source is passed through a filter means into a conical light reflecting member having inner light diffusing surfaces which radially inwardly reflect, mix, and distribute the light rays over an expanded area where they are transmitted through a light diffusing plate. The plate is positioned above one end of a right cylinder mixing chamber provided with means within the chamber for distributing the mixed light to uniformly illuminate a film negative. See U.S. Pat. No. 3,927,941.
Other prior proposed light mixing devices have included a modified hollow sphere having internal diffusely reflecting surfaces provided with a light distributor in the form of a polygonal pyramid or cone for integrating light admitted through a relatively small window and exiting through a larger light exit window (U.S. Pat. No. 3,561,867); a mixing chamber employing a slanted light opaque ceiling and side walls (U.S. Pat. No. 3,756,712); a light integrator box provided with triangular shaped reflectors (U.S. Pat. No. 3,756,719); and an arrangement of light mixing tunnels and light guiding members with light dispersion elements (U.S. Pat. No. 3,492,070).